Doesn't sound like an STD at all- forget about your oral sex exposure as a cause. Could be a fungal infection (e.g. tinea) as you suggested, or a skin irritation or allergic reaction.
See a dermatologist for proper diagnosis and treatment.
i had that problem, it was red and sometimes itched, first on one side then the other, and it would go away then reappear out of nowhere .... now i have weird bumps on my wang... i dont know what from though... hopefully someone can help you more than i can. :[